1. Technical Field
This invention generally relates to filament wound vessels and, more particularly, to metal lined high pressure vessels having an improved structural interface between a metal liner and a polar boss.
2. Background Art
It generally is known that resin impregnated filament wound vessels are capable of withstanding high internal pressures at weight to volume times pressure relationships considerably less than all metal pressure vessels. However, solely filament wound vessels have proven to be too porous to satisfy the criteria required by many military and commercial applications. One approach to solving the problem of unacceptable porosity in a filament wound pressure vessel is to use a metal internal liner. A satisfactory metal lined pressure vessel is disclosed in U.S. Pat. No. 3,843,010, issued Oct. 22, 1974, and owned by the assignee of this invention.
In a metal lined pressure vessel of the character described in the U.S. Pat. No. 3,843,010, a plurality of layers of filaments form an outer shell and are wound about a fitting or boss disposed in an opening in the vessel. The liner is connected to the fitting internally of the shell to prevent leakage between the outer shell and the liner and to prevent leakage through the opening.
Filament wound vessels often are constructed in a spherical or cylindrical shape with generally spherical ends. Due to the rounded geometry of the ends of a pressure vessel in which a polar boss is disposed, cyclic pressurization and depressurization of the vessel causes relative movement between the liner and the boss. Because the liner is impermeably connected to the boss, that is, because the liner necessarily is connected to the boss in such a way that fluid is prevented from escaping from the vessel, the relative movement induces shear stress and fatigue in the liner and can prematurely destroy the vessel.
One approach to joining a metal liner to a polar boss is to bond a ply of resilient material (a shear layer) between the liner and the boss to provide a flexible seal which offers acceptable levels of strain deformation and fatigue cycle life. A bonded shear layer joint of this type is disclosed in the U.S. Pat. No. 3,843,010 discussed above, wherein a pliable interface layer transfers load from the metal liner to a boss. While such a "shear-slip" interface joint is satisfactory for containing many materials, however, exposure of resilient materials such as rubber to many reactive gases and liquids can degrade the integrity of the seal and render this type of design unsuitable for long term storage applications or where very low leakage rates are required.
As an alternative to connecting a metal liner to a polar boss with a resilient shear stress relieving layer, it has been proposed to integrate a metal liner directly with a polar boss, as shown in U.S. Pat. No. 3,815,7773, issued Jun. 11, 1974, and also owned by the assignee hereof. Although integral liners effectively contain gases and corrosive liquids for extended periods of time, such vessels do not afford the high fatigue cycle life inherent in bonded shear layer joint. In addition, the cost of manufacturing unitary metal liners and polar bosses far exceeds the costs incurred in producing liners suitable for use in a bonded shear layer design.
The present invention is directed toward overcoming the above mentioned problems by providing a unique structural interface in a metal lined pressure vessel which exhibits the structural and cost advantages of a bonded shear layer design together with the permeation integrity of a pressure vessel which has an integral metal liner and polar boss.